Mast tilt safety device for lift trucks



June 4, 1968 H. D. RUEB MAST TILT SAFETY DEVICE FOR LIFT TRUCKS Filed Aug. 16, 1965 .llimiii.

up gm r53 A43 firraeue'ys. Means, fisca -4, gas-$544 JZERM United States Patent 3,386,603 MAST TILT SAFETY DEVICE FOR LIFT TRUCKS Harold D. Rueb, Temple City, Calif assignor to Champ Corporation, El Monte, Calif., a corporation of California Filed Aug. 16, 1965, Ser. No. 480,067 3 Claims. (Cl. 214-673) ABSTRACT OF THE DISCLOSURE A lost motion linkage connected between the mast of a lift truck and the mast tilting control mechanism therefor, which stops the movement of the tilting control mechanism at a predetermined forward tilted position of the mast and mechanically moves said mechanism in the opposite direction if the mast tilts beyond the predetermined forward tilted position.

This invention relates to a safety device for a loadcarrying apparatus and, more particularly, to a safety device for fork lift trucks which are particularly suited for the transporting of and stacking of palletized loads. At the present time, one type of fork lift truck used for this purpose includes a tiltable, vertically extending mast which is pivotally mounted on the forward end thereof. A supporting member or fork for carrying such a load is mounted for generally vertical movement along the mast.

In operating a fork lift vehicle, the fork is positioned beneath the palletized load and then elevated to remove that palletized load from the stack or floor upon which it is positioned. To permit rapid handling of materials, the pallet may be carrier at approximately the height of the stack or platform on which the pallet is to be deposited. In proceeding through areas having relatively low vertical clearance, operators of fork lift trucks carrying a palletized load may tilt the mast forwardly of a vertical position to reduce the vertical clearance required. Also, when depositing the palletized load on top of a stack of palletized loads, or on a roof or elevated platform a substantial distance above the ground level, it is frequently necessary or desirable for the mast to be tilted forwardly from a vertical position to an inclined position to allow the pallet or other load carried on the fork to slide off or otherwise be removed from the end of the fork.

When the mast is inclined in the forward direction and the load is carried forwardly of the area of contact between the front tires of the vehicle and the supporting surface for the vehicle, a substantial force or moment tending to tip the entire fork lift truck is exerted thereon. Obviously, this tipping force or moment is increased in proportion to the distance the load is positioned above the vehicle. In some instances, these tipping forces are sufficient to overturn the fork lift truck. As is readily apparent, the tipping of a fork lift truck places the operator and nearby workmen in great danger and may result in damage to the truck, the load carried by the truck, and supplies or equipment which the overturned vehicle may strike.

Accordingly, it is an object of this invention to provide an automatic safety device for use on load-carrying vehicles having a tiltable mast which will prevent the application of a force due to tilting of the mast sufficient to tip the vehicle.

Another object of this invention is to provide a safety device particularly suited for use on fork lift trucks and operable in response to the mast reaching a predetermined forward position. More particularly, the safety device prevents the mast tilting means from tilting the mast forwardly beyond a predetermined forward position.

Another object of this invention is to provide a load 3,386,603 Patented June 4, 1968 carrier having manually operated actuator means for tilting a mast and automatic safety means responsive to the mast reaching a predetermined forward position for overriding the manual operation of the actuator means to control the tilting of the mast. Thus, the safety means makes it impossible for the operator to knowingly or otherwise tilt the mast forwardly beyond a predetermined safe position.

A further object of this invention is to provide a carrier having means for tilting a mast forwardly and safety means responsive to the mast tilting forwardly of a predetermined position for actuating the tilting means to tilt the mast rearwardly.

Briefly stated, the objects of this invention may be accomplished by providing a carrier for carrying a load comprising a support, a mast pivotally mounted on the support and being tiltable forwardly about a pivotal axis from a vertical position to an inclined position, a member mounted on said support for carrying the load, tilting means for tilting the mast forwardly and rearwardly about the pivotal axis, actuator means for causing the tilting means to tilt the mast forwardly, and automatic safety means. The automatic safety means are responsive tothe mast reaching a predetermined forward position for operating the actuator means to prevent the tilting means from tilting the mast forwardly beyond such predetermined forward position. In a preferred. embodiment, the actuator means are manually operated and the automatic safety means override the manual operation of the actuator means to control the operation of the tilting means when the mast reaches a predetermined forward position. Means are also provided for actuating the tilting means to tilt the mast rearwardly or bring it back toward vertical if for any reason the mast should tilt forwardly beyond such predetermined position.

The teachings of the present invention are particularly applicable to a fork lift truck and the specific embodiment described herein shows a safety device utilized with a fork lift truck. It should be understood, however, that the teachings of this invention are applicable to other types of load-carrying devices having a tiltable mast for supporting a load.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing.

In the drawing:

FIG. 1 is a side elevational view of a fork lift truck having a safety device constructed in accordance with the teachings of this invention;

FIG. 2 is an enlarged fragmentary side elevational view partially in section showing the safety device in neutral position and the mast in a substantially vertical position; and

FIG. 3 is an enlarged fragmentary side elevational view similar to FIG. 2 showing the safety device in position to override the manual operation of the tilting means.

Referring to the drawing, the numeral 11 indicates a fork lift truck (FIG. 1) which includes a carrier or vehicle 12 and a mast 13 pivotally mounted about a pivotal axis to the forward end of the vehicle by a shaft 15 (FIGS. 2 and 3). The vehicle 12 which is of the conventional type utilized in transporting loads has front wheels 16 engaging a supporting surface 16a to define an area of contact 1612 therewith.

The mast 13 includes a rear section 17 and a slidable section 19 which is secured to and slidable along the rear section. A supporting member or a fork 21 which performs the load-carrying function is secured to the forward side of the slidable section 19 for movement therealong. Thus, the fork 21 may be moved vertically along the slidable section 19 in the conventional manner. Likewise, the slidable section 19 may be moved vertically along the rear section 17 in a conventional manner. FIG. 1 illustrates in phantom the uppermost positions of the slidable section 19 and the fork 21.

Manually operable means are provided for tilting the mast 13 and the fork 21 as a unit forwardly and rearwardly about the pivotal axis of the shaft 15. The tilting means includes two identical hydraulic cylinders 23 (only one being shown), each having a rod 25 secured to threar end thereof. The vehicle 12 includes a supporting member or chassis 27 having an upwardly extending flange 29 to which one end of the rod 25 is pivotally secured by a pin 31. A piston 33 is slidably mounted within the hydraulic cylinder 23 (FIG. 2) and is secured to a connecting rod 35 which extends out of the hydraulic cylinder toward the mast 13. The forward end of the connecting rod 35 is pivotally secured by a pin 37 to a tab 39 which is rigidly secured to the rear section 17, whereby movement of the piston 33 causes the mast 13 to tilt on the shaft 15.

Actuator means are provided for causing the tilting means to tilt the mast 13 forwardly and rearwardly. The actuator means are partially contained in a housing 4-0 positioned adjacent the forward end of the member 27 (FIGS. 2 and 3) and include a four-way valve 41, a movable actuator member 43, and a manual control lever 45. Four fluid conduits 47 connect the four-way valve 41 to the ends of the two hydraulic cylinders 23. The four-way valve 41 is of a conventional type which will supply a hydraulic fluid to one side of the piston 33 while allowing the fluid on the other side of the piston to escape, thereby causing the desired movement of the piston in a conventional manner. The four-way valve 41 has a first position in which fluid pressure is supplied from a source (not shown) to the piston 33 to tilt the mast 13 forwardly, a second position in which fluid pressure is applied to the other side of the piston 33 to tilt the mast 13 rearwardly, and a neutral position in which the piston 33 is held stationary.

Several suitable linkages may be employed to move the four-way valve between these three positions. In the preferred embodiment illustrated, the extreme downward position of the movable actuator member 43 places the four-way valve 41 in the first position, the uppermost position of the actuator member places the four-way valve in the second position, and an intermediate position of the actuator member, shown in FIG. 2, places the valve in the neutral position. As shown in FIGS. 2 and 3, the movable actuator member 43 is an elongated upwardly extending member which is secured at its lower end to the four-way valve 41 and at its upper end to a manual control lever 45 by a pin 4%. A collar on the movable actuator member 43 limits the downward movement thereof by engaging the valve 41 in the lowest position of the movable actuator member. The manual control lever 45 is generally L-shapcd and is pivotally mounted at its apex to an upstanding flange 51 by a pin 53. The actuator member 43 and the manual control lever 45 may be appropriately constructed as by slotting in the vicinity of the pin 49 to allow free rotational movement of the manual control lever. An operator, by rotating the manual control lever 45 in the clockwise direction, causes the tilting means to tilt the mast 13 forwardly, and by rotating the manual control lever in the counterclockwise direction, causes the mast 13 to tilt rearwardly.

Because any load on the fork 21 is normally carried forwardly of the area of contact 16b, a clockwise tipping moment is exerted about the area of contact 16!). Such tipping moment is counteracted by the weight of the vehicle 12; however, when this moment increases by tilting the load forwardly beyond a predetermined position, it may become a tipping moment which will tip the lift truck forwardly. The lift truck 11 as described hereinabove is subject to such hazardous tipping.

Accordingly, safety means are provided rearwardly of the mast 13 to make is impossible for the operator to knowlingly or otherwise tilt the mast 13 beyond a predetermined safe forward position. The safety means includes an L-shaped link 57, a flexible member or chain 59 which constitutes a lost motion connector and a projection 61 extending laterally of the movable actuator member 43. The L-shaped link is pivotally mounted near its apex by a pin 63 to a tab 65 which is secured to the housing 40. The chain 59 is secured at one end to the upper end of the L-shaped link 57 and at the other end to a finger 67 which is integral with the rear face of the rear section 17. Removable fasteners may be used to secure the ends of the chain 59 to the L-shaped link 57 and to the finger 67 to allow chains of different lengths to be employed as needed or desired. The lower arm of the L-shaped link 57 is positioned beneath the laterally extending projection 61 and is engageable therewith. Thus, clockwise rotation of the L-shaped link 57 causes it to exert an upward force on the projection 61 tending to lift the movable actuator member 43.

The operation of the safety device is as follows. With the mast 13 substantially vertical as shown in FIGS. 1 and 2 and with the safety device in a neutral position as shown in FIG. 2, a load may be picked up and elevated by the fork 21. In transporting the load to a different location while in an elevated position, it may be necessary or desirable to tilt the mast 13 forwardly to reduce the vertical clearance required, or it may be necessary to tip the mast forwadly while the load is elevated in order to remove the load from the fork.

To tilt the mast 13 forwardly, the manual control lever is pushed forwardly or rotated clockwise to depress the movable actuator member 43 to actuate the fourway valve 41 to admit fluid to the left end of the cylinder 23 thereby tilting the mast forwardly about the shaft 15. As the mast 13 tilts forwardly, the chain 59 is tightened. If the Operator knowingly or otherwise maintains the four-way valve 41 in this position, the mast 13 will continue to tilt forwardly until the chain 59 becomes taut. Further tilting of the mast 13 will cause the chain 59 to rotate the link 57 in the counter-clockwise direction so that the lower arm thereof acts against the projection 61 to move the movable actuator member 43 upwardly (FIG. 3).

So long as the four-way valve 41 is in the position, to admit fluid to the left end of the cylinder, the mast 13 will tilt forwardly and as the forward tilting continues, the link 57 tends to raise the movable actuator member 43 an additional amount. Accordingly, the movable actuator member 43 will be raised until the fourway valve is in the proper or safe position in which it does not allow the tilting means to cause any excessive rotational or tilting movement of the mast.

Thus, at a first predetermined forward position, the automatic safety means overrides the manual operation of the actuator member 43 to control the operation of the tilting means. When a second or further forward position of the mast 13 is reached, the safety means will have moved the movable actuator member and the four-Way valve 41 to a proper or safe position. The safety means prevents the tilting means from moving the mast 13 forwardly beyond this second forward position toward an extreme forward position even though the operator may knowingly or otherwise be attempting to rotate the manual control lever 45 clockwise to cause additional forward tilting of the mast. The safety means is so arranged that the second forward position is rearwardly of the positon at which tipping is likely to occur.

When the movable actuator member 43 and the fourway valve 41 are in the proper or safe position, they prevent the tilting means from tilting the mast forwardly. Thus, it will ordinarily be impossible for the mast 13 to tilt forwardly an additional amount after the safety means has moved the movable actuator member 43 to the proper or safe position. However, if for any reason the mast 13 should move slightly forwardly of the second position referred to above, the chain 59 will rotate the L-shaped link 57 an additional amount to cause the actuator member 43 and the four-way valve to move toward a position in which they will cause the tilting means to tilt the mast rearwardly. Thus, if the forward movement of the mast 13 continues, the four-way valve 41 will cause the tilting means to tilt the mast toward the vertical position.

Accordingly, a load-carrying vehicle equipped with a safety device constructed in accordance with the teachings of the present invention contributes substantially to the safety of workmen, equipment, and supplies. Th safety means prevents the operator from knowingly or otherwise operating the actuator means to cause the tilting means to tilt the mast forwardly beyond a predetermined safe position.

Many changes, modifications, and substitutions may be made by those having ordinary skill in the art without departing from the spirit and scope of this invention.

What is claimed is:

1. In a lift truck having a chassis with a vertically extending mast pivotally mounted adjacent the front end thereof, and a load-carrying member mounted on the mast for longitudinal movement relative thereto, the combination of:

means connected to the chassis and the mast for tilting the mast forwardly and rearwardly of a substantially vertical position regardless of the position of the load-carrying member;

control means for the tilting means;

manually operable actuator means on the chassis including an axially movable elongated actuator member attached directly to said control means for actuating the tilting means to cause the mast to tilt forwardly and rearwardly of the substantially vertical position, the movement of said actuator member in one axial direction causing the mast to move in the forward direction and the movement thereof in the other axial direction causing the mast to move in the rearward direction; and

an L-shaped link pivotally mounted on the chassis with one arm thereof in operative engagement with said elongated member intermediate the ends thereof for moving it only in said other axial direction and with the other arm thereof connected to the mast by a lost-motion connector such that the L-shaped link is not actuated thereby until the mast attains a predetermined forward tilted position, whereby when the mast is tilted forwardly beyond a predetermined forward position, said lost-motion connector actuates the L-shaped link to cause it to move the elongated actuator member in said other axial direction and cause the mast to be returned to the predetermined forward tilted position.

2. In a lift truck having a chassis with a vertically extending mast pivotally mounted adjacent the front end thereof, and a load-carrying member mounted on the mast for longitudinal movement relative thereto, the combination of:

means connected to the chassis and the mast for tilting the mast forwardly and rearwardly of a substantially vertical position regardless of the position of the loadcarrying member;

control means for the tilting means;

manually operable actuator means on the chassis including an axially movable elongated actuator member attached directly to said control means for actuating the tilting means to cause the mast to tilt forwardly and rearwardly of the substantially vertical position, the movement of said actuator member in one axial direction causing the mast to move in the forward direction and the movement thereof in the other axial direction causing the mast to move in the rearward direction; and

an L-shaped link pivotally mounted on the chassis with one arm thereof in operative engagement with said elongated member intermediate the ends thereof for moving it in said other axial direction and with the other arm thereof removably connected to the mast by a length of chain such that the L-shaped link is not actuated thereby until the mast attains a predetermined forward tilted position, whereby when the mast is tilted forwardly beyond said predetermined position, said chain actuates the L-shaped link to cause it to move the elongated actuator member in said other axial direction and cause the mast to be returned to the predetermined forward tilted position.

3. In a lift truck having a chassis with a vertically extending mast pivotally mounted adjacent the front end thereof, and a load-carrying member mounted on the mast for longitudinal movement relative thereto, the combination of:

means connected to the chassis and the mast for tilting the mast forwardly and rearwardly of a substantially vertical position regardless of the position of the load-carrying member;

control means for the tilting means;

manually operable actuator means on the chassis including an axially movable elongated actuator member attached directly to said control means for actuating the tilting means to cause the mast to tilt forwardly and rearwardly of the substantially vertical position, the movement of said actuator member in one axial direction causing the mast to move in the forward direction and the movement thereof in the other axial direction causing the mast to move in the rearward direction;

a bracket fastened to the mast in an exposed position in substantial horizontal alignment with said actuator member;

an L-shaped link pivotallymounted on the chassis with one arm thereof in operative engagement with said elongated actuator member intermediate the ends thereof for moving it only in said other axial direction and the other arm positioned .in the direction of the mast; and

an elongated connector having one end thereof connected to said other arm and the other end removably fastened to said bracket, whereby when the mast is tilted forwardly beyond a predetermined forward position, the connector actuates the L-shaped link to cause itto move the elongated actuator member in said other axial direction and cause the mast to be returned to the predetermined forward tilted position.

References Cited UNITED STATES PATENTS 2,178,368 10/1939 Dunham 214-673 2,208,954 7/1940 Weiss 214-673 2,301,832 11/1942 Towson et al. 214673 ROBERT o. SHERIDAN, Primary Examiner.

GERALD M. FORLENZA, Examiner.

R. B. JOHNSON, Assistant Examiner. 

